The objectives of this study are twofold. The first is to develop and extend the dynamic light scattering technique so that it may be used to study some important biological problems. The second is to use the technique for extensive study of particular systems, especially membrane model systems. Three main areas of research will be pursued: (1) The development of a "light scattering label" technique to allow one to study the scattering from one component in a complex mixture or of one part of a large molecule or aggregate, (2) the study of translational, orientational and local relaxation times of biological macromolecules or aggregates in solution (such as myosin, ATCase). These quantities will be used to obtain the shape and solution dimensions of molecules in solution. Furthermore, they will be used in combination with nuclear magnetic resonance and electron paramagnetic resonance techniques to obtain information about local structure and dynamics of molecules, (3) the morphology and fusion of important membrane model systems, phospholipid vesicles, will be studied by applying the techniques (1) and (2) above as well as ultracentrifugation techniques.